Embodiments of the present invention relate to printing, and particularly to a pressure damping ink filter for use in a continuous ink jet printer.
Continuous ink jet printers are well known in the field of industrial coding and marking, and are widely used for printing information, such as expiry dates, on various types of substrates passing by the printer on production lines. Ink jet printing allows ink to be deposited or printed at pre-determined locations on a substrate so as to create desired images, shapes, forms, or characters, without requiring physical contact between the printing device and the substrate.
Conventional ink jet printers may include an ink source, an electric fluid pump, an orifice or orifices (nozzles), a charging tunnel, and deflection electrodes. The ink may be pressurized by the electric fluid pump, which draws the ink from the ink source and pushes the ink through the nozzle. The ink droplets may then be discharged from the nozzle in the form of a filament, which subsequently may break up into a droplet stream. The stream of ink passing through the nozzle may also be broken up into a regular stream of uniform ink drops by an oscillating piezoelectric element. The stream of ink drops may then pass through a charging field, such as that generated by one or more charged electrodes, wherein the individual drops of ink may be charged to selected voltages. The charged droplets may then pass through a transverse electric field, or deflection field, created in the space between a pair of deflection electrodes. Each charged ink droplet may then be deflected by an amount that corresponds to the degree of its respective charge, which may then allow the droplet to be projected at its intended location on the substrate so as to assist in forming the desired image. If the ink droplet is uncharged, it may pass through the deflection electrodes without deflection. Uncharged or slightly charged droplets may be collected in a catcher and returned to the ink source for reuse.
The quality of printing by an ink jet printer is dictated by several factors, including ink pressure. Fluctuation in ink pressure may cause droplets of ink that have been discharged through the nozzle to shift in position as the droplets pass through the charging field. A shift in position in the charging field may result in the ink droplets receiving an improper charge, i.e. an insufficient or excessive charge. The improperly charged ink droplets may then be misdirected by the deflection electrodes, thereby causing the ink to be deposited at an unintended location on either the substrate, which may result in a bad image formation, or on print-head components, which may eventually cause a device failure, such as a high voltage, no signal, or phasing fault.
One common problem of conventional ink jet printers is that the electrical fluid pumps that are used to pressurize the ink stream may generate high frequency pulses, i.e. pressure surges. To alleviate these pressure fluctuations, some ink jet printers utilize a physically large filter medium and accumulators that are housed in a large container, or filter housing. The larger sizes of these systems require that the system use a high volume of ink. The increased size of the filter medium and volume of ink may minimize the effect of pressure fluctuations from the pump. However, the relatively large size of the filter medium and volume of ink required may reduce the effectiveness of these systems, and may also increase operating and construction costs. Further, the large ink volume in these systems increases the chances that a greater portion of ink will go unused before its period of usefulness expires, in which case larger volumes of unused ink may be wasted.
Other pressure damper devices that attempt to reduce or eliminate ink pressure fluctuations in ink printers include a combination of diaphragms and restrictors. Such pressure damper devices may contain moving parts, such as springs and valves. However, the moving parts of such pressure damper devices may be damaged and/or fail as their components come in contact with the ink or other fluids. Further, over a period of time, these moving parts may also degrade, which may result in a reduction in the pressure damper device's ability to effectively maintain the desired pre-set operating ink pressure. These pressure damper devices are also often relatively large in size and costly.
Thus, a need exits for a system of damping ink pressure fluctuations for use in ink jet printing. Overall, a need exists for an efficient and cost-effective system for damping pressure fluctuations in the ink stream of ink jet printers.